1. Field of the Invention
The present invention generally relates to impact instruments including hammering devices such as claw hammers, ball-pein hammers, axes, hatchets, sledges, and the like, and also including recreational devices such as croquet rackets, badminton racquets, tennis racquets, racquetball racquets, golf clubs, baseball bats, softball bats, cricket bats, hockey sticks, and the like. An embodiment of the invention relates to an impact instrument having an improved mass distribution. Another embodiment relates to an impact instrument that includes a handle that focuses the contact of the hand onto a more limited region. Another embodiment relates to an impact instrument that includes a pivoting handle. Yet another embodiment relates to an impact instrument having a handle that dampens and/or decreases shock and vibration. These embodiments may be used independently or in combination to increase the peak impulse produced by the impact instrument and/or to decrease or dampen shock/vibrational forces felt by a user of the instrument.
2. Description of the Related Art
FIG. 1 illustrates a conventional hammer 10 that includes a head 12 and a shank 14 extending from the head. The head terminates at one end in an impact surface 18 through which the hammer delivers an impulse during use. An actual pivot point 16 exists on the shank about which the hammer is pivoted or rotated in the hand during use. Hammers are typically grasped in a user""s hand(s) during use and so pivot point 16 may actually be an extended pivot (i.e., a pivot region) rather than a point pivot, since the hammer pivots about a region of finite width (i.e., a hand). Nevertheless the center of this extended pivot region is generally the pivot point 16. When the hammer is grasped in the hand, pivot point 16 may be approximated to lie at a point along the shaft that is proximate the center of the middle finger of the hand. Obviously the pivot point 16 varies depending on where the hand is grasping the shank 14.
The center of impact surface 18 is separated from pivot point 16 by a vertical distance d as illustrated in FIG. 1. The center of percussion is located at a distance b from pivot point 16. The center of percussion is the point at which an impulse could be applied in a direction perpendicular to shank 14, thereby causing shank 14 to pivot about a point, such that there is minimal (in a real world application) or no force (ideally) that is perpendicular to the longitudinal axis of the shank. It should be noted that the center of percussion is not necessarily the same as the center of mass. In most objects the center of percussion is not the same as the center of mass.
The radius of gyration is separated from the actual pivot point by a distance k. The radius of gyration, k, is the distance from the actual pivot point to a location at which the mass of the hammer could be concentrated without altering the rotational inertia of the hammer about the actual pivot point. The locations of the radius of gyration and the center of percussion both depend upon the actual pivot point and the mass distribution of the hammering device. The moment of inertia, I, the radius of gyration, k, and the mass of the hammering device, m, are related by the following equation: I=mxc2x7k2. The center of mass of the hammer is located at a vertical distance h from pivot point 16.
The xe2x80x9cideal pivot pointxe2x80x9d is defined as follows for the purposes of this application. It is believed that distance b will always be equal to k2 divided by h (i.e., k2/h). Thus the xe2x80x9cideal pivot pointxe2x80x9d is when b, as calculated by the equation b=k2/h, is equal to d. Stated another way, for an impact instrument the ideal pivot point is the pivot point where the center of percussion coincides with the center of the impact surface. In most cases, the xe2x80x9cideal pivot pointxe2x80x9d 20 exists at a location (e.g., on an elongated member) where an impulse could be applied in a direction perpendicular to the elongated member, thereby causing the elongated member to pivot about a point, such that there is no reactive force that is perpendicular to the longitudinal axis of the elongated member at that point.
Conventional impact instruments (e.g., hammers) tend to have an ideal pivot point that does not coincide with pivot point 16 when held by the typical user. That is, during normal use the center of percussion does not typically coincide with the center of the impact surface of a conventional impact instrument (e.g., hammer), which tends to make use of the impact instrument (e.g., hammer) inefficient and uncomfortable. The amount of vibration felt by the user tends to increase as the vertical distance between the actual pivot point and the ideal pivot point increases. In most conventional hammers, for instance, the ideal pivot point is often displaced from the actual pivot point in a direction toward head 12. For hammers that weigh about 1-2 pounds, the ideal pivot point is frequently between about 0.3 cm and about 3.0 cm removed from the actual pivot point.
During use of a hammering device, it is generally desirable to grasp the hammer at a location such that at least a portion of the hand is proximate or at least in the vicinity of the end 17 of the hammer as shown in FIG. 1. Grasping the hammer proximate the end allows the user to impart a given impulse to a target object with relatively less effort than if the hammer is grasped at a location that is higher up on the shank in a direction towards the head. If the hammer were grasped at the ideal pivot point of a conventional hammer, the xe2x80x9cmoment lengthxe2x80x9d between the hand and the impact surface would be shortened, tending to result in more inefficient use of the hammer.
It is desirable that an improved impact instrument be derived to deliver a greater impulse and reduce vibration and shock imparted to the user of the device.
U.S. Pat. No. 4,870,868 relates to a sensing device that produces a response when the point of impact between an object and a member occurs at a preselected location on the member.
U.S. Pat. No. 5,289,742 to Vaughan relates to a shock-absorbing device for a claw hammer to dampen vibrations occurring through a steel hammer head.
U.S. Pat. No. 5,375,487 to Zimmerman relates to a maul assembly having a maul head with an annular body that is partially filled with a quantity of flowable inertia material.
U.S. Pat. No. 5,259,274 to Hreha relates to an internally reinforced jacketed handle for a hand tool.
U.S. Pat. No. 5,362,046 to Sims relates to vibration damping devices placed in the butt end of implements which are subject to impact.
The above-mentioned patents are incorporated herein by reference.
In accordance with the present invention, an impact instrument is provided that generally eliminates or reduces the aforementioned disadvantages of conventional impact instruments.
An embodiment of the invention relates to a hammering device that includes a head and a shank extending from the head. The head has an impact surface adapted to deliver an impulse to an object during use. The shank may terminate opposite the head in an end and preferably includes a grasping region in the vicinity of the end. The mass distribution throughout the hammering device is preferably such that when the hammering device is grasped within the grasping region during use, the center of percussion of the device coincides with the impact surface. An impact point is preferably centrally-disposed on the impact surface, and the center of percussion preferably coincides with the impact point during use.
Another embodiment of the invention relates to an impact instrument that includes an impact surface for delivering an impulse to an object. A shank or elongated member extends from the head and may extend substantially along a longitudinal axis. The impact instrument preferably includes a sheath substantially surrounding a portion of the shank. A cavity that contains compressible material is preferably formed between the sheath and the shank. When an object is struck with the impact surface, the shank may compress a portion of the compressible material, allowing the sheath to pivot with respect to the longitudinal axis of the shank. The sheath may lie along an axis that is substantially parallel to the longitudinal axis of the shank when the impact instrument is at rest.
The ideal pivot point is usually located at some point on the shank. During use of the instrument, the pivoting of the grasping member (e.g., a sheath) may cause the axis of the grasping member to form an angle with the longitudinal axis of the shank. The pivoting of the grasping member preferably occurs about the pivot point such that the formed angle has a vertex at the ideal pivot point and is less than about 10xc2x0. The pivoting of the grasping member preferably increases the impulse delivered to the object and decreases vibration and shock imparted to the user. The compressible material preferably dampens any vibrational forces, further reducing vibration felt by the user. The pivoting of the grasping member may also allow the rotational motion of the hand to continue at the moment of impact to reduce counter-rotational forces, shock, and stress imparted from the hammering device to the user.
The grasping member may surround the shank to form a substantially annular cavity where the compressible material is contained. The annular cavity may have a cross-section that is circular or non-circular. An inner member may be disposed between the compressible material and the shank. The inner member preferably surrounds the shank to form the annular cavity between the member and the sheath. The thickness of the cavity may vary along the length of the shank. The thickness of the cavity is preferably at a minimum proximate the ideal pivot point and may increase along the shank as the distance from the pivot point increases. The grasping member or sheath preferably rigidly contacts the shank solely at or in the region of the ideal pivot point. At other points along the shank, the compressible material preferably separates the grasping member (e.g., sheath) and the shank.
The compressible material may be disposed completely around the perimeter of a cross-section of the shank to allow the sheath to pivot with respect to the shank. The shank may comprise a front and a side, and the sheath may be adapted to pivot about the front of the shank to form an angle of about 3-7 degrees, and more preferably 5 degrees, between the axis of the sheath and the front of the shank. The sheath is preferably adapted to pivot about the side of the shank to form an angle of about 5 degrees between the axis of the sheath and the side of the shank.
The impact instrument may be a relatively small hand tool having a mass between about 1 pound and about 3 pounds. The impact surface and the elongated member may comprise metal, plastic, polycarbonate, graphite, wood, fiberglass, other similar materials, or a combination thereof. The hammering device may include a substantially rigid, non-pivoting butt located at the end of the shank to facilitate the pulling of nails. The impact instrument may be a hammering device (e.g., ball-pein hammer, maul, bricklayer""s hammer, scaling hammer, sledge, hatchet, ax, etc.), a recreational device (e.g., croquet mallet, racquetball racket, badminton racket, tennis racket, golf club, softball bat, cricket bat, baseball bat, hockey stick, etc.), or any hand-held instrument that ordinarily is swung by a human to deliver an impulse to an object.
An advantage of the invention relates to an impact instrument having an impact surface that coincides with the center of percussion during use.
Another advantage of the invention relates to an impact instrument adapted to pivot about an ideal pivot point to increase the impulse (e.g., the peak impulse) delivered by the instrument during use.
Another advantage of the invention relates to increasing the effective moment length of a impact instrument without lengthening its elongated member to increase the total impulse delivered from the device.
Yet another advantage of the invention relates to an impact instrument adapted to pivot about an ideal pivot point to decrease vibrations and shock imparted from the instrument to the user.
Another advantage of the invention relates to a pivoting impact instrument that reduces fatigue experienced by a user of the instrument.
Still another advantage of the invention relates to a handle that dampens vibrations felt by the user through the handle.
Another advantage relates to an impact instrument that pivots to reduce reactive forces and stress exerted by the instrument on the user, thereby reducing incidents of stress disorders such as xe2x80x9ctennis elbow.xe2x80x9d